The Spreadsheet Import builder is attempting to interpret the data as date values instead of numeric values when a WEF application is deployed as a portlet.
WEF includes poi 2.5.1, and portal includes an older version of poi. The portal version HSSFDateUtil.isCellDateFormatted method returns true incorrectly for a number of cell format strings which it shouldn't. (formats 164-173) This causes the spreadsheet data to be incorrectly interpreted as date values.
Resolving the problem
You can resolve this issue by forcing WEF exported portlet .war files to include the 2.5.1 version of jakarta-poi.jar.
The exclude line in portlet7.0.excludes should be removed to allow jakarta-poi.jar to be included in our .war files.
Find this files here:
This is a simple text file which you can edit it in Eclipse or any text editor. You will need to remove the following line from the file:
Then save the excludes file and perform an Export->Web Experience Factory Portlet WAR action to generate a new .war file that contains the jakarta-poi.jar library.